What is Stent Thrombosis?
Stent thrombosis is a condition where a blood clot forms and blocks a coronary stent – a tiny mesh tube that keeps a coronary artery open. This is a serious problem that can happen when treating blocked arteries in the heart, using a procedure called percutaneous coronary intervention (PCI). Stent thrombosis can lead to severe health issues or death, often causing a heart attack.
This issue is often compared to in-stent restenosis, which results in chest pain, while stent thrombosis leads to more severe conditions like acute coronary syndrome (ACS). People with a history of diabetes, ACS, or impaired heart function are at increased risk of developing stent thrombosis.
In 2008, specific guidelines were created to classify stent thrombosis. This classification is based on the type of stent used, the patient’s situation, and the time following the stent placement. The types of stents include bare-metal, and first- and second-generation drug-eluting stents which slowly release medicine to help keep the artery open.
Depending on when it happens after the stent placement, stent thrombosis is classified as:
- Acute, if it occurs within 24 hours.
- Subacute, if it’s between 24 hours and a month.
- Early, if it happens within one month.
- Late, if it’s between 1 and 12 months.
- Very late, if it happens after 12 months.
Stent thrombosis can either cause symptoms or not cause any noticeable issues. Silent occlusion refers to unexpected stent blockage without any signs or symptoms. The seriousness of stent thrombosis can be classified as:
- Possible, if the cause of death is unknown, 30 days or more after stent placement.
- Probable, if the cause of death is unknown within 30 days of stent placement, or if there’s evidence of inadequate blood supply to a part of the heart on an electrocardiogram (EKG).
- Definite, if a blood clot in the stent is confirmed through tests, with symptoms like sudden ischemic symptoms at rest, new ischemic changes on an EKG, a typical rise in cardiac markers, or evidence of a blood clot at autopsy or via thrombectomy.
What Causes Stent Thrombosis?
Large studies and health records have found that certain patient characteristics, aspects of the procedure, or attributes of the stent are linked to an issue known as stent thrombosis, which is a blood clot in the stent.
The Champion-phoenix trial, a type of study, found factors like Non-ST-elevation myocardial infarction (NSTEMI) and ST-elevation myocardial infarction (STEMI) – two types of heart attacks- at the start of symptoms, presence of a blood clot seen during the procedure, and the total length of the stent were each pointers for acute stent thrombosis, meaning a blood clot in the stent shortly after the procedure.
Another study, named Acuity, found other factors associated with a higher likelihood of stent thrombosis. It listed diabetes, weak kidneys, the Duke jeopardy score (a measure of the risk involved in heart operations), the final smallest internal width of the stent once it is in place, the use of a certain medication (thienopyridine) before the process, the hemoglobin level at baseline, and the amount of heart disease were each independent factors of stent thrombosis shortly after the procedure.
The Horizon AMI trial, which looked at detailed images of heart arteries, found that if the stent has enough space to open up fully, if it was placed correctly, if blood clots or plaque didn’t stick out, if there weren’t any small tears on the edge of the stent, and if the artery was not still narrowed, then this predicted a lower chance of stent thrombosis. The study showed that if a stent is placed in an artery branch, it also contributes to stent thrombosis.
Finally, the Triton TIMI 38 trial showed that patients with STEMI are at higher risk of stent thrombosis no matter what type of stent is used. However, a more effective antiplatelet medicine named prasugrel reduced that risk by 50%. Antiplatelet medications help to prevent blood clots from forming in the stent.
Risk Factors and Frequency for Stent Thrombosis
Stent thrombosis is a complication that can occur after a stent has been inserted into a blocked blood vessel. Earlier studies found that up to 16% of patients experienced this complication. Furthermore, between 15% to 30% of patients who developed stent thrombosis unfortunately passed away within the first month of the event. Doctors initially tried using various medications like acetylsalicylic acid, dipyridamole, coumadin, and dextran to prevent stent thrombosis.
Nowadays, the combined approach of using two kinds of antiplatelet drugs and inflating the stent with a higher pressure has greatly reduced the rates of stent thrombosis. The rate now is about 0.7% within the first year, and then drops further to a range of 0.2% to 0.6% in the following year. For procedures performed to prevent a heart attack, the rate of stent thrombosis is even lower, ranging from 0.3% to 0.5%. However, when the procedure is performed in response to an acute coronary syndrome, like a heart attack, the rate of stent thrombosis can be higher, up to 3.4%.
Interestingly, the type of stent used doesn’t appear to change the overall rate of stent thrombosis. Both bare-metal stents and drug-eluting stents (which release medication to prevent blockage) have similar rates. The only difference is the timing of when the thrombosis might happen. Bare-metal stents tend to have a peak risk at about 30 days, whereas drug-eluting stents have their peak risk around three months, or possibly later, depending on the specific drug used on the stent.
Signs and Symptoms of Stent Thrombosis
When a patient who recently underwent a procedure to open up their heart’s blocked arteries (known as percutaneous coronary intervention) experiences chest pain (angina), medical professionals typically take several steps to diagnose the issue. These include:
- Reviewing the patient’s medical history and medication use
- Performing a laboratory test for P2Y12 resistance
- Performing a 12 lead EKG
- Doing an echocardiogram to look for new movement abnormalities in the heart wall
- Testing of cardiac enzymes in the laboratory
About 60% of patients who have a blood clot in their heart’s stent (referred to as stent thrombosis) come in with a certain sort of heart attack called STEMI. The rest 40% typically present with different types of heart attacks or unstable angina. Those patients with the STEMI type heart attack as a result of stent thrombosis tend to have higher chances of dying while in the hospital (around 17.4%). Moreover, such patients who develop this blood clot issue soon after the intervention are more prone to develop a potentially fatal condition where the heart can’t pump enough blood (cardiogenic shock) compared to the ones who develop stent thrombosis late or very late. However, it’s quite unlikely that a patient who doesn’t present an acute heart syndrome would show stent thrombosis in further performed coronary angiograms.
Testing for Stent Thrombosis
If your doctor suspects that you’re experiencing chest pain (angina) after a recent procedure to widen your blood vessels (coronary stenting), they will rely heavily on their professional judgement to evaluate your condition. You will likely undergo several examinations.
Firstly, your doctor will listen to your medical history and do a physical examination. This can help them understand what might be causing your chest pain. In addition, you will undergo an EKG, which is a test that measures the electrical activity of your heart to identify any problems. This will be followed by an echocardiogram, a test that uses sound waves to create detailed images of your heart, allowing your doctor to observe its size, shape, and how well it’s working.
Your doctor may also test your blood for cardiac enzymes. These proteins are released into the blood when the heart muscle is damaged. A high level of these enzymes can indicate a heart-related issue, such as a blockage of your blood vessels.
In extreme cases, like a severe heart attack (STEMI), you might have to undergo an urgent procedure called coronary angiography. In this test, a special dye is injected into your blood vessels and X-rays are taken. This allows the doctor to see any blockages or narrowing in the vessels that supply blood to your heart.
Treatment Options for Stent Thrombosis
If you are having an angiography, a procedure to see how blood flows through your arteries, your doctor may need to clear a clot in a blocked vessel to restore normal blood flow. This is done through processes called aspiration thrombectomy or angioplasty.
Your doctor will also check if your body is responding well to the medication you’re taking. If not, you may need a stronger antiplatelet drug — these are medicines that help prevent blood clots. Examples of these drugs are prasugrel and ticagrelor.
Usually, after getting a drug-eluting stent (a small, metal mesh tube that expands inside a coronary artery), you’d have to continue taking two different antiplatelet drugs for a year. If you got a bare-metal stent (a stent without a coating of medication), you’d have to take these drugs for at least a month.
The doctor will then evaluate the stent placement by using specialized imaging techniques like intravascular ultrasound (IVUS) or optical coherence tomography (OCT). These tools help the doctor determine how well the stent is placed, if it’s expanded properly, and if there are any issues with the edges of the stent. If needed, the doctor will adjust the stent’s position and fix any problems with the edges to prevent the stent from developing a clot again.
It’s important that the doctor tries to avoid putting in additional stents if possible. This is because each additional part of the stent may increase the chance of a clot forming in the stent.
What else can Stent Thrombosis be?
When trying to identify a specific medical condition, doctors consider several possibilities. One possible diagnosis that they might explore includes:
- In-stent restenosis, a condition in which an artery previously widened with a stent – a tiny tube – narrows again, causing chest pain similar to angina (a type of heart-related chest pain).
Stent thrombosis, a condition where a blood clot forms in a stent, usually leads to acute coronary syndrome (ACS), a term for situations where the blood supplied to the heart muscle is suddenly blocked. Meanwhile, instances of ACS in the body’s natural vessels – not those with stents – should also be ruled out.
What to expect with Stent Thrombosis
Stent thrombosis, a condition when a blood clot forms in a stent placed in a heart artery, is linked to high rates of illness and death, often resulting in heart-related death or a nonfatal heart attack. It’s usually more urgent and critical than in-stent restenosis, which causes chest discomfort or chest pain.
Stent thrombosis often leads to acute coronary syndrome (ACS), a term we use to describe conditions where blood flow to the heart is suddenly blocked. The prognosis or the likely course of this disease improves tremendously if it’s identified and treated early. High vigilance from clinicians, and a detailed patient history, are crucial for a timely and accurate diagnosis.
Possible Complications When Diagnosed with Stent Thrombosis
Stent thrombosis, or clot formation in a cardiac stent, is a significant issue related to the use of stents in cardiac treatments involving opening of narrowed or blocked heart arteries. If not properly managed, the occurrence of stent thrombosis may lead to critical outcomes like death, heart attack, and shock where the heart fails to pump enough blood.
Moreover, the treatment of stent thrombosis can also present its set of complications, similar to those observed in cardiac stent placement. These can involve:
- Bruising or discoloration at the site of stent placement
- Formation of a solid swelling of blood within the tissues, known as a hematoma
- Development of a pseudoaneurysm or an abnormal blood-filled dilation of the blood vessel
- Bleeding into the internal cavities near your lower back
- Abnormal heart rhythms, known as arrhythmia
- Nephropathy caused by contrast media used during diagnostic imaging
- Formation of additional blood clots
- Infection
- Stroke as a result of blood clot cuts off blood supply to the brain
- Myocardial infarction, another term for a heart attack
Preventing Stent Thrombosis
After undergoing a procedure called PCI (Percutaneous Coronary Intervention), where a device called a DES (Drug-Eluting Stent) is placed to help keep heart arteries open, patients should be aware of risks. One such risk is stent thrombosis, which is the forming of a clot around the stent, especially in the initial period after the operation.
Patients should also know that if they experience any typical anginal symptoms such as chest discomfort or signs of acute coronary syndrome like sudden chest pain or pressure, they should go to the emergency department immediately for further checks. It’s crucial to take these symptoms seriously and get medical help immediately.
